Nix Module Bulk Edit

Nix Module Bulk Edit

Reliable patterns for bulk-editing Nix module files in a project like devenv.

When to use

• Adding a new config line/block to many language modules
• Updating template references across many files
• Any repetitive Nix file modification across a directory

Pitfalls

1. Don't use execute_code Python scripts for bulk file writes

The sandbox can run out of disk space (OSError: [Errno 28] No space left on device). Use terminal with perl or sed instead.

2. Don't use patch tool for Nix files with complex indentation

The patch tool's fuzzy matching often fails on Nix due to subtle whitespace differences. Use terminal with perl -i -0pe for reliable multi-line replacements.

3. Always verify Nix option paths

In devenv, gitnr is config.gitnr, NOT config.integrations.gitnr. Using the wrong path causes: The option 'integrations' does not exist. Check the module's options block to confirm the exact path.

4. Verify template existence before committing

Many assumed templates don't exist. Always check:

• GitHub main: https://api.github.com/repos/github/gitignore/contents/
• GitHub community:

https://api.github.com/repos/github/gitignore/contents/community

• GitHub global: https://api.github.com/repos/github/gitignore/contents/Global
• TopTal: https://www.toptal.com/developers/gitignore/api/list

5. Handle multi-line blocks carefully

When removing previously-added blocks, use perl -0pe with /s flag:

perl -i -0pe 's/^\s+integrations\.gitnr\."\.gitignore"\.templates =
  \[\n.*?\];\n//gms' file.nix

Workflow

1. Map first: Build a complete mapping of file → template before editing
2. Verify options first: Use search.nixos.org or the module docs to

confirm the exact NixOS option path before editing

1. Prefer direct module options: If a module exposes a native option, use it

instead of raw environment.etc / tmpfiles plumbing

1. Clean first: Remove any previously-added incorrect lines
2. Apply: Use terminal + perl for bulk insertion
3. Verify: grep or a module-specific check to confirm correct lines exist
4. Build: Run the relevant rebuild/build command to validate

Nix style

• Prefer short-hand attr syntax when it stays readable and accurate.
• Keep YAML-shaped Nix attrsets close to the final manifest shape; avoid

unnecessary wrapper layers.

• For RKE2 manifests on NixOS, prefer services.rke2.manifests with target +

content over manual environment.etc and systemd.tmpfiles.rules.

See references/rke2-manifests.md for the option shape and the RKE2 manifest pattern.

NixOS module editing notes

• Prefer services..manifests, services..settings, or similar

native options when the module already supports generated configuration.

• Use raw filesystem staging only when the module has no native declarative

hook.

• For RKE2, services.rke2.manifests..content can generate YAML directly,

and target controls the manifest filename under /var/lib/rancher/rke2/server/manifests.

• Keep generated YAML minimal and explicit; avoid extra tmpfiles indirection

when the module can write the file itself.

• For already-formatted external disks on hosts, prefer fileSystems with

by-label/by-uuid and nofail + x-systemd.automount; see references/external-disks-by-label.md.

• See references/rke2-manifests.md for the concise option shape and the

manifest-generation pattern.

Example: Adding gitnr to language modules

# Step 1: Clean any previous attempts
for f in $(grep -rl 'integrations\.gitnr\|gitnr\.' src/modules/languages/); do
  perl -i -0pe 's/^\s+integrations\.gitnr\."\.gitignore"\.templates =
    \[.*?\];\n//gm' "$f"
  perl -i -0pe 's/^\s+integrations\.gitnr\."\.gitignore"\.templates =
    \[\n.*?\];\n//gms' "$f"
done

# Step 2: Add correct line (example for go.nix)
perl -i -pe 's/(config = lib\.mkIf cfg\.enable \{)/$1\n
  gitnr.\".gitignore\".templates = [ \"gh:Go\" ];/' src/modules/languages/go.nix

# Step 3: Verify
grep -rn 'gitnr' src/modules/languages/

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: shikanime-labs
• Source: shikanime-labs/skills
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.